A successful FMEA begins with a clear structure analysis. The AIAG-VDA 7-Step FMEA Handbook recommends breaking down the subject into System, Subsystem, and Component levels.
👉 This hierarchical approach helps the FMEA team:
- Define relationships between elements.
- Identify interfaces where failures often occur.
- Ensure no critical part or process is overlooked.
What is System, Subsystem, and Component Breakdown? #
- System – The highest-level product or process under analysis.
- Subsystem – Major building blocks that make up the system.
- Component – The smallest elements or parts within a subsystem.
📌 For PFMEA, this hierarchy applies as Process → Process Step → Work Element.
Why Breakdown is Important in FMEA #
- Provides clarity on what exactly is being analyzed.
- Helps avoid confusion and duplication during Function & Failure Analysis.
- Simplifies complex designs or processes into manageable levels.
- Enables traceability from high-level functions down to specific parts.
Example 1 – DFMEA: Electric Motor #
- System: Electric Motor Assembly
- Subsystems:
- Rotor
- Stator
- Housing
- Bearings
- Components:
- Rotor: Shaft, Laminations, Permanent Magnets
- Stator: Windings, Core, Insulation
- Housing: Covers, Seals
- Bearings: Inner/outer rings, Lubrication
👉 This breakdown helps the DFMEA team analyze risks at each level (e.g., winding insulation failure, bearing seizure).
Example 2 – PFMEA: Welding Process #
- Process (System): Spot Welding Operation
- Process Steps (Subsystems):
- Load components
- Position components
- Apply electrode force
- Apply current
- Release and unload
- Work Elements (Components):
- Operator handling
- Fixture alignment
- Electrode condition
- Current supply
👉 This breakdown helps the PFMEA team identify risks at the operator level, equipment level, and environment level.
Example 3 – FMEA-MSR: Braking System Monitoring #
- System: ABS (Anti-lock Braking System)
- Subsystems:
- ECU
- Wheel Speed Sensors
- Hydraulic Modulator
- Components:
- ECU: Microcontroller, Software, Power Supply
- Sensor: Magnet, Wiring, Connector
- Modulator: Valve, Pump
👉 The breakdown ensures the team considers hardware + software + sensor integration risks.
Best Practices for Breakdown #
- Use structure trees for system-level FMEAs.
- For processes, always prepare a Process Flow Diagram before PFMEA.
- Keep the breakdown consistent with FMEA scope defined in Step 1.
- Capture interfaces (System ↔ Subsystem, Subsystem ↔ Component).
- Don’t go into unnecessary micro-detail (avoid listing screws, washers, etc., unless safety-critical).
Common Mistakes to Avoid #
- Jumping straight to failures without structure breakdown.
- Over-detailing → analysis becomes unmanageable.
- Ignoring interfaces (e.g., ECU ↔ Sensor connections).
- Not aligning breakdown with APQP/DFMEA/PFMEA templates.
Case Study – Suspension Assembly PFMEA #
- System: Front Suspension Assembly
- Subsystems: Shock Absorber, Control Arm, Spring, Bushings
- Components:
- Shock Absorber: Tube, Piston, Oil Seal
- Control Arm: Arm Body, Ball Joint
- Spring: Coil Material, Heat Treatment
- Findings: Team identified that oil seal leakage could cause shock absorber failure, which was missed in earlier generic process reviews.
Key Takeaways #
- System = Entire product/process
- Subsystem = Major functional blocks
- Component = Detailed parts/work elements
- Breakdown ensures clarity, completeness, and traceability.
- A structured breakdown is the foundation for Function and Failure Analysis (Steps 3 & 4).
Next Lesson #
👉 Continue with Lesson 3.3.2: Process Flow → Structure Tree & Block Diagram
